MgO Protective Layer Research Articles

Application of MgO/ZrO2 coating on 309 stainless steel to increase resistance to corrosion at high temperatures and oxidation by an electrochemical method

Abstract 309 stainless steel is one of the steels that have the highest resistance to corrosion and thermal oxidation compared to other steel grades, but it should not be used at temperatures higher than 980°C if there are temperature fluctuations. Additionally, 309 stainless steel is not designed for use in wet environments and has the least corrosion resistance. This study aims to cover 309 stainless steel with MgO/ZrO2 particles using a two-step electroplating deposition method and then sintering to increase its resistance to wet corrosion and oxidation in temperature fluctuations. The intermediate ZrO2 coating makes the outer MgO layer about two times thicker and reduces the corrosion current density. The morphology of the coatings was determined using scanning electron microscopy and X-ray diffraction, and oxidation resistance was determined using cyclic oxidation tests and the wet corrosion test of the corrosion solution. 3.5% NaCl was used. The results showed that the coated samples, due to the use of TiO2 middle layer and MgO protective layer in the electrochemical method, have a 2-fold increase in wet corrosion and an increase in hardness of about 77%, as well as an increase in oxidation resistance of 1.8% compared to the sample without coating. Also, the reason for using the electrochemical deposition method is for better surface smoothness and less porosity of the coating as well as its use on all metals compared to thermal spray methods.

Improving corrosion resistance of Mg–Li alloys by Sn microalloying

It is well known that the corrosion resistance of ultra-light Mg–Li alloys is inferior to traditional Mg alloys due to the rapid oxidation of reactive Li on the surface. In this study, microalloying Sn has been found to improve the corrosion resistance of Mg–Li alloys due to the formation of Mg2Sn on the corrosion pits and reduction of electro-potential difference. Indeed, the addition of Sn not only reduced the corrosion rate to the minimum value of 4.27 mmpy but also promote the formation of dense corrosion oxide films. The volt potential difference between the matrix (α-Mg and β-Li) and Al-X (Gd, Y, Mn) phases has also been measured to reduce from 260 mV (α-Mg) and 343 mV (β-Li) to 220 mV (α-Mg) and 220 mV (β-Li). After homogenization, pitting was significantly reduced, as shown by the in-situ observation of the corrosion process using X-ray tomography. By quantifying the secondary phases, it has been found that the corrosion expansion was restricted by the Mg2Sn and Al-X phases. The corrosion products are primarily MgO, SnO, and Li2O oxides and the corrosion mechanism follows three stages: I. Breakthrough of MgO protective layer by corrosive fluid; II. Hydrogen evolution reaction (HER) between matrix phase and water immersion; III. Segregation of secondary phases and corrosion products. It has been found that all three processes are highly dependent on the Sn solutes and Mg2Sn precipitates, showing the bright future development of corrosion-resistant Mg–Li alloys by Sn microalloying.

Monte Carlo simulations of MgO and complex oxide protective thin layers bombarded with noble-gas ion in plasma discharge devices

The lifespan of plasma discharge devices is strongly influenced by the deterioration characteristics of MgO protective layer deposited on the dielectric covering the electrode. In order to attain both lower driving voltage and higher luminous efficiency in these devices, different complex metal oxides protective layers have been extensively studied as alternatives to MgO. However, the interaction between energetic ions and fast neutral atoms with the protective layer can produce serious damages to it and their nearby components. In this paper, we study the ion beam bombardment for several protective layers by low-energy noble gas with various ion incidence angles by using the Monte Carlo simulation. On the basis of the binary collision approximation using SRIM-2013, different parameters are discussed for instance backscattering yield, retained dose, sputtering yield, number of vacancies, and ion range of MgO, (Mg,Ca)O, (Mg,Sr)O, (Mg,Ba)O and (Mg,Ca,Sr)O. From our results, the retained dose, sputtering yield and number of vacancies of complex metal oxide protective layers are lower than that of MgO. Moreover, the backscattering yield increases by increasing the incident angles and it is highest for complex metal oxide protective layers.

Annealing process for recovery of carbonated (Mg,Ca)O protective layer for plasma discharge device

The carbonation behavior and decarbonation annealing of a protective (Mg,Ca)O layer for flat panel plasma discharge devices were investigated. Compared with a conventional MgO protective layer, the (Mg,Ca)O protective layer showed both high and low discharge voltages. Quantitative X-ray photoelectron spectroscopy analyses indicated that the high discharge voltages were caused by Ca carbonation. The progression of Ca carbonation was enhanced by exposure to air containing H2O but not by exposure to dry air. In addition, once (Mg,Ca)O is carbonated, it is impossible to decarbonate Ca by annealing in air at the temperature applied during the production process. We propose the use of annealing in vacuum as an effective method to promote the decarbonation of Ca and maintain a low discharge voltage for plasma discharge devices with (Mg,Ca)O protective layers.

Monte Carlo simulations of MgO and Mg(OH) 2 thin films sputtering yields by noble-gas ion bombardment in plasma display panel PDP

Abstract MgO is known to be a material suitable for barrier coating of commercial plasma display panel (PDP) cells owing to its excellent electrical insulating property, good resistance to sputtering, large secondary-electron emission coefficient and high transmittance. It is also a valuable information for improving the efficiency and the lifespan of the PDP. However, the effect of moisture emitted from the wall and phosphor materials of the PDP cells, an Mg(OH)2 is formed on the top surface of an MgO protective layer. In this work, the Monte Carlo simulation program SRIM-2013 was applied to calculate the sputtering yields of magnesium hydroxide Mg(OH)2 by low-energy noble-gas ion bombardment. The comparison between results obtained by Monte Carlo simulation and those obtained by experiments is elucidated in this paper. Furthermore, the surface binding energies for MgO and Mg(OH)2 layers on sputtering yield are discussed. It is found that the sputtering yield of Mg(OH)2 is generally lower than that of MgO at each incident energy. On the other hand, the sputtering yield depends on the properties of both the incident particle and the target.

Electro-optical Characteristics of the Degraded Functional Layer in an Alternating- Current Plasma Display Panel

The electro-optical characteristics of several functional layers over the MgO protective layer were studied during the continuous discharge of an AC-PDP. In order to observe the degradation of each functional layer on the MgO protection layer, we measured the surface morphology, cathodoluminescence (CL) spectrum, the secondary electron emission coefficient (γ) and the discharge characteristics after 500 hours of discharge during the operation of the AC-PDP.

Comparative study of micro-arc oxidation treatment for AM, AZ and MZ magnesium alloys

This paper introduces a novel coating process based on micro-arc oxidation (MAO) for formation of ceramic MgO layer over some newly developed magnesium alloys in an environmentally friendly electrolyte by anodization. Electrochemical corrosion testing showed that the corrosion resistance of bare AMS4429 is much better than that of AZ31HP-O and MZ due to formation of protective Nd-rich oxide layer in AMS4429 compared to less protective Al- and Zn-rich oxide films for AZ31HP-O and MZ respectively. Surprisingly, the corrosion resistance of MAO coated MZ is about 50 times higher than the bare one. The deposition, characterization and electrochemical characteristics of the fine porous MgO protective layer formed due to MAO coatings were investigated in details.

Effect of gold nanorods in an MgO protective layer of AC plasma display panels.

We propose a modified MgO protective layer for alternating current plasma display panels. The modified MgO protective layer of the panel tested here has a structure that incorporates silica-coated Au nanorods (NRs), leading to localized surface plasmon resonance (LSPR) in the near-infrared (IR) region. The silica-coated Au NRs were synthesized by a simple chemical method and inserted into an MgO protective layer using an air-spray method. The operating voltage of the proposed structure was decreased by 10 V. The luminance and luminous efficacy of the test panel part with the silica-coated Au NRs both increased by about 15%. According to the measured results of the IR response time, the sustain discharge time lag was reduced. In addition, by inserting the silica-coated Au NRs into the MgO protective layer, a decrease of the IR emission proceeding from the plasma discharge was acquired. Finally, we investigated the LSPR effect of the silica-coated Au NRs in a simulation with a finite-difference time domain method.

Fabrication and characteristics of LaB6-doped MgO protective layer for plasma display panels

Lanthanum hexaboride (LaB6) doped MgO film was fabricated by the magnetron sputtering method as a new protective layer for alternating current plasma display panel (AC PDP). Surface morphology, optical properties and discharge characteristics were discussed by varying LaB6 doping concentration. It was demonstrated that this film was effective in decreasing the firing voltage of AC PDP. Especially when the LaB6 doping concentration was 3%, the firing voltage was reduced by 17% compared with the conventional MgO layer under 10% Xe–Ne of 400Torr. The results suggest that this new protective layer is beneficial to decrease the electrical power consumption of AC PDP.

Formation of a Compact Protective Layer by Magnesium Hydroxide Incorporated with a Small Amount of Intumescent Flame Retardant: New Route to High Performance Nonhalogen Flame Retardant TPV

Magnesium hydroxide (MH) and an intumescent flame retardant (IFR) have been incorporated into a thermoplastic vulcanizate (TPV) for the purpose to fabricate halogen-free flame retardant elastomeric materials. Significant synergistic effects of MH and IFR have been observed for the TPV in terms of both flame retardant properties and mechanical performance. The mechanism of the synergistic effects has been investigated. The results indicate that a small amount of IFR accelerates the degradation of the matrix and induces a shrinkage matrix, leading to a compact and unbroken MgO protective layer. Such compact MgO layer on the surface of the material prevents the bulk material from further degradation, and a high flame retardant performance was achieved. Obviously, this novel flame retardant system paves new possibility for the high performance nonhalogen flame retardant polymeric materials and should also be applied to other polymers.

Lowering of the firing voltage and reducing of the discharge delay time in alternating current plasma display panels by a discontinuous spin-coated LaB6 film on the MgO protective layer

A spin coated LaB6 discontinuous film is covered on MgO protective layer to improve the discharge performance of alternating current plasma display panels. Under the premise of high transmittance of more than 90%, a very small amount of polycrystal LaB6 powders added in an organic solvent are chosen as the coating solution. The discharge characteristics results show that with 250 torr 5% Xe-Ne pressure, the firing voltage and discharge delay time of the test panel with LaB6/MgO double protective layer are decreased by 13.4% and 36.5%, respectively, compared with that of conventional MgO protective layer, likely owing to the low work function of LaB6. Furthermore, the aging time of the proposed structure is comparable to that of pure MgO protective layer. Therefore, it will not increase the production costs and is highly suitable to be applied for alternating current plasma display panels with low electrical power consumption.

Effects of Sc- and Zr-doped MgO layers on electron emission and discharge characteristics of alternating-current plasma display panels

To improve the material properties of a protective layer for alternating-current plasma display panels, a small amount of Sc or Zr was added to a conventional MgO protective layer. The electrical properties and surface characteristics of the Sc and Zr doped MgO protective layers deposited by an ion plating method were investigated. Experimental results show that the secondary electron emission coefficients of the Sc and Zr MgO protective layers are higher than those of conventional MgO protective layers, resulting in the reductions in firing voltage and address discharge delay time. To elucidate the reason for the increase in secondary electron emission, the changes in work function and energy band structure were investigated by cathodoluminescence (CL) measurement and ultraviolet photoelectron spectroscopy (UPS). The measurements show that the work functions of the Sc and Zr MgO protective layers markedly decreased in comparison with that of the conventional MgO protective layer. Experimental results reveal that the secondary electron emission has a strong correlation with the change in work function or energy band structure that is related to the defect level produced by doping, thereby resulting in changes in electrical discharge voltage and delay time.

Exoemission Properties of PDP Protective Layers

The priming properties of four different types of protective layers inside plasma display panels (PDPs) are compared, using undoped MgO, Si-doped MgO, Sc-doped MgO, and MgCaO (15%) plasma protective layers. In a two-electrode type of PDP, the statistical spread in discharge formation time is measured, as a function of the waiting time from 5 μs to 50 ms, after excitation by a different number of sustain cycles (1-1024) at 200 and 10 kHz. The results are interpreted in terms of the delayed emission of exoelectrons from these oxide cathodes. The kinetics of the emission process is compared with that of the existing recombination emission models. An exocurrent contribution is present in all of the materials that decays with the square root of the waiting time. It is proportional to the electron density itself, and can qualitatively be explained by a three-particle Auger electron loss mechanism.

Cubic-Shaped Al-Doping MgO Powders Used in PDPs

In order to improve the secondary electron emission coefficient of MgO, we propose to dope Al into MgO. The precursor was obtained by hydrothermal method in the condition of different reaction temperature, different filling volume and different reaction time by using urea, Mg (CH3COO)2and AlCl3. The Al-doping MgO crystallites powders were obtained by calcining the precursor. The crystal phase and morphology of the products were characterized by XRD and SEM. The results showed that the Al-doping MgO powders were cubic-shaped crystallites. The discharge characteristics of Al-doping MgO powders were tested in a chamber as when the panel was sealed in Ne and 7% Xe at 450 torr. As expected, the discharge voltage of the panel is lower with the Al-doping MgO protective layer than without that.

The Fabrication of Screen-Printed Lanthanum Hexaboride Films Applied in PDP Protective Layer

In this paper, a screen-printed LaB6discontinuous film is coated on the MgO protective layer to meet the market for low power requirement of AC PDP. The surface appearance, optical transmittance and conductivity properties of the screen-printed LaB6/MgO double protective film are studied by changing the slurry contents and annealing temperature. It is found that when the mass ratio of LaB6powder in the printed slurry is 1%, the transmittance of the film is above 90% with excellent insulation properties. The SEM shows that LaB6particles are randomly distributed on the smooth MgO layer surface and distances among LaB6islands are at least several micron dimensions. Besides, XRD patterns indicate that when the annealing temperature is 500°C, the LaB6film exhibits a strong preferred orientation to the (100) plane, which is beneficial to improve the performance of AC PDP.

Improvement of Discharge Properties by Printing ${\rm LaB}_{6}$ Films on MgO Protective Layers in Plasma Display Panel

In this letter, a screen-printed LaB6 discontinuous film is coated on MgO thin film to improve the discharge properties of MgO protective layer in alternating current plasma display panel (AC PDP). High transmittance of is obtained by adjusting the concentration ratio of polycrystal LaB6 powders and organic solvent of screen-printed slurry. The LaB6/MgO double protective layer almost shows lower firing voltage and shorter discharge delay time than conventional MgO protective layer, likely owing to the low work function of LaB6. Therefore, it is highly suitable to be applied for AC PDP with low electrical power consumption.

Effects of pressure and electrode resistance on AC-plasma display panels (AC-PDPs) for various panel temperatures

In this study, the effects of panel temperature on AC-plasma display panels (AC-PDPs) were investigated. Macroscopic properties, such as the luminance, discharge delay time lag, and discharge current decreased while the breakdown voltage increased with increasing panel temperature. These data implied that changes in the materials properties with the panel temperature strongly affected the macroscopic properties, including the gas-discharge characteristics of AC-PDPs. The reason can be explained by the change in the collision kinetics due to the increase in the pressure in the AC-PDPs, the voltage drop due to the increase in the resistivity of the metal electrodes, and the decrease in the effective voltage due to the decrease in the surface resistivity of a MgO protective layer. The properties of other components such as the indium-tin-oxide (ITO) transparent electrode and the dielectric layer changed little in the considered temperature range (0 ∼ 80 °C), and, thus, are not thought to affect the macroscopic properties of AC-PDPs with changing panel temperature.

The Influence of the Defect States on the Secondary Electron Emission from the Mg1-x BexO Protective Layer of AC Plasma Display Panels

In order to improve the material properties of the protective layer for alternating current plasma display panels, small amount such as BeO elements was added to the MgO protective layer. The electrical properties of Mg1-xBexO film deposited by an electron beam evaporation were investigated. The experimental results reveal that the discharge voltage of PDP device with the Mg1-xBexO film, when the concentration of BeO was 40 at.%, was reduced by 20 V, compared with the conventional MgO film. To elucidate the reason for increasing the secondary electron emission, the change in the energy band structure was investigated by measuring PL. The experimental results show the defect level of the Mg1-xBexO films increases to a large extent in comparison with that of the conventional MgO film. It also implies that the secondary electron emission has a strong correlation with the energy band structure, related to the defect levels originating from doping and thence resulting in changes in the associated electrical characteristics.

Changes in ionization potentials of MgO and CaO films upon heating in air and vacuum investigated by metastable de-excitation spectroscopy

Changes in the ionization potential of MgO and CaO film surfaces upon heating in air and vacuum, which are necessary processes in the manufacture of plasma display panels, were investigated by metastable de-excitation spectroscopy. Heating at 500°C for 1min in vacuum is effective for cleaning an MgO film surface previously heated in air, resulting in the recovery of the ionization potential of the cleaned MgO surface from the increased value upon heating in air. A similar treatment is not effective for the CaO surface. This difference in behavior can be attributed to the stronger bonding states of H2O and CO2 on CaO than those on MgO. This is consistent with the fact that CaO has not yet been practically used as a protective layer in plasma display panels. Furthermore, the firing voltages of the plasma predicted for the MgO and CaO protective layers from the ionization potentials determined by metastable de-excitation spectroscopy were found to qualitatively agree with measured firing voltages obtained for a test panel. The present results confirmed that metastable de-excitation spectroscopy is effective for evaluating protective layers used in plasma display panels.

Spin relaxation mechanism in silver nanowires covered with MgO protection layer

Spin-flip mechanism in Ag nanowires with MgO surface protection layers has been investigated by nonlocal spin injection using permalloy/Ag lateral spin valves. The spin flip events mediated by surface scattering are effectively suppressed by the MgO capping layer. The spin relaxation process was found to be well described in the framework of Elliott-Yafet mechanism (R. J. Elliott, Phys. Rev. 96, 266 (1954); Y. Yafet, in Solid State Physics, edited by F. Seitz and D. Turnbull (Academic, New York, 1963), pp. 1–98) and then the probabilities of spin-filp scattering for phonon or impurity mediated momentum scattering is precisely determined in the nanowires. The temperature dependent spin-lattice relaxation follows the Bloch-Grüneisen theory (V. F. Bloch, Z. Phys. 59, 208 (1930); V. E. Grüneisen, Ann. Phys. 5, 530 (1933)) and falls on to a universal curve of Ag as in the conduction-electron-spin resonance data for bulk.